Power screwdrivers for use in successively driving screws which are collated, secured in a parallel spaced relation with a belt or plastic strip of material are known. One such power screwdriving apparatus is described in U.S. Pat. No. 4,146,071 to Mueller et al, issued Mar. 27, 1979, the disclosure of which is incorporated herein by reference. Such known power screwdrivers include a rotatable and reciprocally moving screwdriver shaft, which is turned in rotation by an electric motor. A screwdriving bit held in an end-most portion of the shaft, defines a tip for engaging the head of each successive screw as it is moved into a driving position, axially aligned under the screwdriving shaft.
In the driving position, a cup-shaped screw locating member is provided to support a peripheral edge of the screw head. The screw locating member typically defines a radial extent of a boreway through which the shaft and screw head axially move as the screw is driven. The boreway preferably having a diameter marginally larger than the outside radial diameter of the head of the screw.
The shaft is axially movable in the boreway in a reciprocal manner to engage the screw and drive it into a work-piece. After each screw is driven the shaft retracts and a subsequent screw carried on the strip is advanced sideways into the boreway, engaging the locating member so as to be axial aligned under the shaft. The shaft typically has a diameter equal to or slightly smaller than the diameter of the screw head so as to not adversely wear against the locating member as each screw is driven.
Known power screwdrivers suffer the disadvantage in that the locating member is often fixed relative to the shaft, making it impractical to use the screwdriver with screws having different diameter screw heads. For example, on insertion of a screw having a head diameter appreciably larger than the diameter of the boreway, the screw abuts the locating member in a position out of axial alignment with the shaft and driving bit. Similarly, the use of screws having a head diameter appreciably smaller than the diameter of the axial boreway also results in the screw abutting the screw locating member at a position out of axial alignment with the shaft and driving bit. In either case, the tip will not properly engage the head of the screw resulting in premature tip wear, or causing the screw to deflect out of the correct axial orientation necessary to be driven.
To adapt the power screwdrivers for accommodating various sized screw heads, the screw locating member could be made movable radially inwardly and outwardly relative the boreway. In addition to adding to the cost of production, providing a movable locating member is disadvantageous in that the cup-shape of the locating member is fixed and is selected to engage the peripheral surface of only one diameter screw head. Accordingly, screws having screw heads which are either too small or too large may not be provided with adequate support by the locating member. Additionally, use of a movable locating member in accommodating screws having smaller head diameters, may result in a shaft and/or bit designed for use in driving screws having a larger head diameter, to disadvantageously wear against the locating member.